Vbscript & programming Newbie

Sorry if my question is silly & useless. Pls answer me. I am lost.

I just started programming.
I am making a shopping cart. Where the data is stored in mdb. And the website list it and we can select the what we want and add it to a cookie.
My question is:
I am seen in websites with links like:

I was trying to make a page like that(with the “?” thing). I am using server side includes(ssi).
the page i made is:
index.asp has the other 3 files like ssi in it.
Now my question is:
in the header.asp, there is 2 category. Click which, i should get a list of all the items in the category.
now when i load “index.asp”, it should load header.asp, footer.asp & body.asp. but when i load “index.asp?category=1”, then it hould load header.asp, footer.asp & category1.asp.
I looked around for tutorial on how to do it. But i could not find it. Can some one pls tell me how to do it or give me a sample from which i can learn or just tell me what is the technical term for this and what should be my search term in google. If i doing all in the wrong way, pls correct me.
I think its very easy, because i see it everywhere. So, pls excuse my silly question and pls help me out

Thanks for your time